Austentic alloys



March 6, 1962 Filed June 25, 1959 EL a RA STRENGTH, PSI x 10 D. J.SCHMATZ AUSTENITIC ALLOYS 2 Sheets-Sheet 1 ULTIMATE ULTIMATE SILICONDUANE J. SCHMATZ INVENTOR.

6. BY MzxM ATTORNEYS March 6, 1962 D. J. SCHMATZ AUSTENITIC ALLOYS 2Sheets-Sheet 2 Filed June 23, 1959 ULTIMATE ULTIMATE SILICON SILICONDUANE J. SCHMATZ QIIIVZLK EIYTOR. M

ATTORNEYS United States Patent 3,024,103 AUSTENITIC ALLOYS Duane J.Schmatz, Dearborn, Miclm, assignor to Ford Motor Company, Dearborn,Micl1., a corporation of Delaware Filed June 23, 1959, Ser. No. 822,2784 Claims. (Cl. 75-124) This invention relates to the siderurgical artand more particularly is concerned with the provision of an austeniticalloy which is fabricated from inexpensive and non-critical elements andwhich has good physical and oxidation resistant properties attemperatures up to 15 00 F. This invention is further concerned with aprocedure for imparting to metal articles produced from this alloy asurface which is more resistant to high temperature oxidation than theinterior of the article. i

This alloy is essentially composed of iron, aluminum, manganese, siliconand carbon with residual amounts of insignificant impurities. I

Two figures of drawing have been supplied for aid in understanding theproperties of these alloys.

FIGURE 1 includes four graphs showing the ultimate tensile strength,yield point, reduction of area and elongation of an alloy producedaccording to this invention at 1100 F. and 1200 F.

FIGURE 2 includes four graphs showing the ultimate tensile strength,yield, point reduction of area and elongation of the alloy shown inFIGURE 1 at the temperature values of 1350 F. and 1500 F.

In search for face centered cubic alloys containing little or nocritical and expensive elements, the iron base alloys containing sevento thirteen percent aluminum have been exhaustively studied. To rendersuch ordinarily body centered alloys face centered, resort was had tothe addition of twenty to forty percent manganese and 0.10 to 1.10percent carbon. These alloys were prepared by melting in vacuo in azirconium crucible. After the aluminum was added, helium was introducedin the melting chamber and the additions of manganese were made. Thispractice prevented excessive loss of manganese. The melts were cast intoten pound ingots 2% inches in diameter and then rolled at 2100 F. intoinch round bars. A basic alloy of 9 percent aluminum, 30 percentmanganese and 1.0 percent carbon appeared to be the most promising.

Contrary to ordinary metallurgical consideration, silicon was found tobe the only element which could be added to this basic composition toimprove both the oxidation resistance and strength without drasticallyreducing the ductility. The highly desirable results flowing from theaddition of one to two percent of silicon to the basic alloy is shownclearly by a careful study of FIG- URES 1 and 2 of the drawing which arethought to be self-explanatory. The basic alloy upon which thesedrawings were predicated comprised 8 percent aluminum, 30 percentmanganese and 1.0 percent carbon. Attention is particularly invited tothe critical and beneficial efiects of this amount of silicon upon thecharacteristics 60 of the alloys at 1350 F. and 1500 F. as shown in FIG-URE 2 of the drawings.

3,024,103 Patented Mar. 6, 1962 These alloys are also susceptible to agehardening. This characteristic of these alloys is shown by the followingtable.

The resistance of articles fabricated from these alloys to hot oxidationmay be improved by impoverishing the surface layer as to the readilyoxidizable elements carbon and manganese with a concomitant enrichmentof the surface with respect to aluminum. This is accomplished by heatingthe article in an oxidizing atmosphere at a temperature above that whichwill be encountered in service. This heating removes a substantialportion of the manganese and carbon from the surface and leaves asurface which is essentially a highly oxidation resistant iron aluminumalloy.

The desired results are obtained when one to two percent silicon areadded to the basic alloy described above. However, very good results areobtained if the basic alloy corresponds to the composition, 8 to 10percent aluminum, 20 to 35' percent manganese and 0.75 to 1.10 percentcarbon.

I claim:

1. An austenitic alloy which is resistant to atmospheric oxidation attemperatures up to 1400 F. and which consists essentially of 8 to 10percent aluminum, 20 to 35 percent manganese, 0.75 to 1.10 percentcarbon and 1.0 to 2.0 percent silicon, the remainder being iron andincidental impurities.

2. An austenitic alloy which is resistant to atmospheric oxidation attemperatures up to 1400" F. and which consists essentially of 9 percentaluminum, 30 percent manganese, 1 percent carbon and 1.5 percentsilicon, the remainder being iron and incidental impurities.

3. The process of increasing the resistance to oxidation of an alloyconsisting essentially of 8 to 10 percent aluminum, 20 to 35 percentmanganese, 0.75 to 1.10 percent carbon and 1.0 to 2.0 percent silicon,the remainder being iron and incidental impurities comprising exposingthe alloy to an oxidizing ambient at a temperature substantially abovethe contemplated operating temperature to impoverish the surface of thealloy with respect to manganese and carbon.

4. A highly oxidation resistant alloy steel article the bulk of whichconsists essentially of 8 to 10 percent aluminum, 20 to 25 percentmanganese, 0.75 to 1.10 percent carbon and 1.0 to 2.0 percent silicon,the surface of said article being substantially impoverished withrespect to manganese and carbon whereby its oxidation resistance isincreased.

References Cited in the file of this patent UNITED STATES PATENTS

1. AN AUSTENITIC ALLOY WHICH IS RESISTANT TO ATMOSPHERIC OXIDATION ATTEMPERATURES UP TO 1400* F. AND WHICH CONSISTS ESSENTIALLY OF 8 TO 10PERCENT ALUMINUM, 20 TO 35 PERCENT MANGANESE, 0.75 TO 1.10 PERCENTCARBON AND 1.0 TO 2.0 PERCENT SILICON, THE REMAINDER BEING IRON ANDINCIDENTAL IMPURITIES.